Sensor according to the runtime principle with a detector unit for mechanical-elastic waves

ABSTRACT

A detector unit apparatus and method for operating and producing a detector unit to be adapted to varying environmental influences or to its own, in particular mechanical, electrical or magnetic parameters of the detector unit, which are dependent on measuring lengths. An inventive positional sensor operating according to the running time principle of a mechanically elastic shaft and comprising a waveguide, a positional element, e.g. a positional magnet, which can be displaced in particular along the waveguide, in addition to a detector assembly that is located on the waveguide and comprises a detector coil wherein the detector assembly has a current source so that a current can flow through the detector coil.

I. AREA OF APPLICATION

The invention concerns position sensors, in particular their detectorunit, based on the principle of the runtime measurement ofmechanical-elastic impulses in a waveguide, which include, beside thiswaveguide, a position element that can move relatively to it and that isgenerating or detecting the mechanical-elastic wave.

II. TECHNICAL BACKGROUND

The waveguide usually consists of a pipe, a wire or a strip, and canserve also as an electrical conductor. The waveguide can be arrangedfurther in a form-giving, linear or circular body made of non-magneticmaterial, e.g. plastic or metal, for the support and bearing of thewaveguide.

Based on the Wiedemann effect, a current pulse fed into the waveguideproduces, by its overlaying with a laterally on the magnetostrictivewaveguide oriented external magnetic field, which is originating from aposition element, in particular from a position magnet, generates atorsion impulse of a mechanical elastic wave which spreads out in bothdirections in the waveguide, with approximately 2,500 m/s-6,000 m/s fromthe place of generation, that means e. g. the position of the positionelement—depending upon the elastic modulus or the shear modulus of theused waveguide material.

In a place, usually at an end of the waveguide, the torsion part of thismechanical elastic impulse is sensed in particular by a detector unit,which is located in most cases in a fixed position related to thewaveguide. The time duration between the release of the exciting currentimpulse and the receipt of this mechanical-elastic wave is thereby ameasure for the distance of the movable position element, e.g. of theposition magnet, from the detector unit or also from the coil and/orelectromagnet.

Such a typical sensor is described in the U.S. Pat. Nos. 5,590,091 aswell as 5,736,855.

The main attention of the present invention is on the detectorarrangement. This covers a detector coil, which is either arrangedaround the waveguide or is arranged as a so-called Villary detectoraround a Villary strip, which is standing away crosswise, in particularin a 90° angle, from the waveguide and is connected with it in a way, inparticular mechanically, e.g. by welding, that the torsion impulserunning in the waveguide is transformed in the Villary strip into alongitudinal wave. Such a longitudinal wave compresses respectivelystretches the magnetoelastic element, which means the waveguide or theVillary strip, in an elastic way within the crystalline range, andchanges therefore its permeability μ. The Villary strip respectively thewaveguide consists for this purpose of a material with as high a changeof the magnetic permeability Δμ_(r) as possible e.g. from nickel or anickel alloy, or from other suitable materials. As a compromise betweenthe looked for characteristics also the so-called constant module alloyshave proven with which the temperature coefficient of the E and/or shearmodules are influenceable and in particular can be kept constant overwide temperature ranges. Thereby for instance the form of a self-stablestrip material is selected with a thickness of approximately 0.05-0.2 mmand a width of 0.5-1.5 mm.Because${{{\Delta\quad U} \approx {N \times \frac{\Delta\quad\Phi}{\Delta\quad t}}}->{{\Delta\quad U} \approx {N \times \frac{\Delta\quad B \times \Delta\quad A}{\Delta\quad t}}}} = {N \times \frac{\mu_{0} \times \Delta\quad\mu_{r}}{\Delta\quad t} \times \frac{I \times N}{L}}$therefore${\Delta\quad U} \approx {\frac{\Delta\quad\mu_{r}}{\Delta\quad t} \times K}$because the values for μ₀, I, N, L can be considered as being constant.

The mechanical elastic density wave passing through a magnetoelasticelement, e.g. the Villary strip, expresses itself thus in a voltagevariation ΔU, which can be measured as a useful signal at the detectorcoil.

As it is evident, the useful signal ΔU is the larger, the larger thevariation of the magnetic permeability Δμ_(r) results.

Additionally such a range of the curve Δμ_(r)(H), thus of the magneticpermeability over the magnetic field strength, is desired as operatingpoint or operating range in which the magnetic permeability Δμ_(r)changes as linear as possible, however as strongly as possible relativeto the reason, and therefore it will be tried to configure the functionΔμ_(r)(H) in the rising slope as steeply as possible and to establishthe working area there, within the approximately linear range.

In the state of art a so-called bias magnet in form of a permanentmagnet is arranged in spatial proximity to the detector coil, e.g.parallel to the Villary strip, to adjust the operating point.

The operating point of the mechanical-elastic detector unit depends,besides from the magnetic parameters of the bias magnet, mainly on itspositioning relative to the detector coil.

This is in unfavorable in several respects, for instance with employmentof the position sensor in places, which are subjected to mechanical, inparticular dynamic mechanical loads or also thermal loads, which changethe magnetic parameters of the bias magnet and accelerate in particularits aging process, which entail likewise a change of the magneticparameters.

Additionally all form deviations from the normal shape, arising with themanufacturing of the bias magnet, are unfavorable in the same way. Thesame applies to the production-determined dispersions of the magneticparameters with the manufacturing of the bias magnet.

A further disadvantage consisted in the fact that in case of a too closeapproach of the position magnet to the detector coil, the operatingpoint is changed negatively. Therefore, with the detector unit inaccordance with the state of the art, the waveguide had to be extendedover the measuring range, within whose the position magnet could moveback and forth, so far that the detector unit with the detector coil wasfar away enough from the measuring range in order to reduce disturbinginfluences to a controllable extent. This however always resulted in anoverall length of the position sensor, which was clearly larger than itsmeasuring range.

In the following the configuration of the detector unit as a Villarydetector and as a coaxial detector unit will be described, withoutlimiting the invention on that, since this is also applicable with adetector coil arranged coaxially around the waveguide. The solution asVillary detector has the advantage of a particularly strong suppressionof externally linked, mechanical-acoustic spurious signals inrelationship to the useful position signal.

III. PRESENTATION OF THE INVENTION

a) Technical Problem

It is therefore the task in accordance with the present invention, tomake available a detector unit, in particular a Villary detectorrespectively a detector coil around the waveguide, as well as aprocedure for its operation and manufacturing, which avoids thedisadvantages of the state of the art and in particular permits anadaptation of the detector unit to changing environmental influences orto changing own parameters, in particular mechanical, electrical ormagnetic, measuring length-dependent parameters of the detector unit.

b) Solution of the Problem

This problem is solved by the characteristics of the claims 1, 3, 6 and38. By subjecting the detector coil with a bias current, a bias magneticfield is produced that is variable at any time.

If the power source is adjustable, the bias magnetic field can becontrolled in this way and external influences, aging processes etc. canbe compensated and the detector unit can be operated at the desiredoperating point, preferably within the range of a linear dependencebetween magnetic permeability and mechanical traction/compressionstress.

If additionally or instead of that one or more flux guiding pieces arearranged at the detector coil, then this causes on the one hand a closedmagnetic circuit through the coil and on the other hand a shieldingagainst disturbing external magnetic fields, like those who canoriginate, for example, from the position magnet or also from themagnetic field around the waveguide itself, and the linking ofdisturbing impulses is substantially reduced. Such influences arisewithout shielding by a flux guiding body before all if the positionmagnet approaches the detector unit, so that for this reason, withconventional position sensors, a relatively large dead range must beconsidered, thus a length range in the proximity of the detector unit,which the position magnet must not enter. This causes a larger overalllength of the position sensor in relationship to the desired measuringlength and is therefore disadvantageous with many applications.

The flux-guiding piece has also the function to reduce the controlcurrent (bias current) to a minimum as well as to increase the signalamplitude.

The magnetic shielding in form of the flux guiding body should therebyconsist of a material with an as high magnetic permeability as possible(μ_(r)>>1), in particular at least μ_(r)>1000, in order to need a lowcontrol current. Alternatively the flux guiding body can be alsomagnetically hard, in order that even without current flow through thedetector coil a residual magnetic field remains by remanence and theflux guiding body acts at least for a limited time as a bias magnet(temporary permanent magnet).

Particularly in cases, in which the flux guiding body respectively theflux guiding bodies do not completely enclose the detector coil and/orif no flux guiding pieces are used, but also as an additional measure,the magnetic shielding can be improved by a shield housing, whichencloses the detector coil as tightly as possible including the part ofthe magnetic-elastic element (waveguide or Villary strip) that ispenetrating it. As material for the shield housing the so-calledMu-metal is applicable, which possesses a permeability of μ_(r)>1000.

As far as the detector unit has the design of a Villary detector, thatis with a Villary strip standing away crosswise from the waveguide,which extends into the detector coil, preferably also out of it again,then the flux guiding body must contain necessarily at least oneentrance opening, and also an exit opening for the Villary strip ifnecessary, and the Villary strip must be movable without mechanicalcontact in relationship to it. Beyond that at least one conductoropening is necessary in the flux guiding body, in order to be able toinsert the electrical conductors supplying the detector coil into theflux guiding body. Preferably this is done not through the openings forthe Villary strip, but via a separate conductor opening, which is alsoin the front face of the usually cylindrical flux guiding bodies,preferably however in their lateral surface.

In order to make possible a simple assembly of the flux guiding body,the flux guiding body consists either of two half-cylindrical shells,completing each other to a cylinder, in which the described openings arelocated on the contact face of the half shells, or of a pot-shapedcylinder open on a face, and a face closing cover.

Furthermore it is to be made certain that the waveguide, and itssurrounding and supporting body if necessary, is located in a definedposition to the detector coil, and this relative position issufficiently strongly immovable, fixed.

The detector unit includes a detector arrangement, in which the detectorcoil is integrated, and beyond that also a power supply.

The detector coil and the uncoupling impedance can then beinterconnected either in a measuring bridge, or in a series circuit, inorder to get the desired useful position signal, which afterwards can bepreferably processed over a difference amplifier and if necessary, afurther bridge circuit. The two coils are preferably realized as twoseparated coils e.g. on a common spool. Combining into only one commoncoil is possible.

While the Villary strip consists in all rule of magnetoelastic material,multipart configurations are also possible from a first and a secondpartial strip, which are connected together, whereby then preferably thefirst partial strip does consist of non-magnetic and non-magnetoelasticmaterial, the second partial strip, in turn, of magnetoelastic material.

In order to reduce the influence of the detector unit by the exciterimpulse as far as possible, the bias current of the detector coil isonly connected after the exciter impulse faded away through thewaveguide. Afterwards the bias current is either controlled in orderthat the Villary strip can be operated within the linear range asdescribed above, or in order that the attainable useful position signalbecomes optimal, in particular regarding its absolute amplitude and/orin relationship to the strength of the disturbing position signal.

The configuration of the detector coil in form of a toroidal coil, inparticular if it is flowed through by current, has proven itself asparticularly effective, above all, for the adjustment of the operatingpoint, whereby the central opening of the toroidal inductor ispenetrated then by the magnetoelastic element, that is the Villary stripor the waveguide, since thereby a particularly good useful signal isobtained.

Furthermore it has shown that also the detection of the useful signal ispossible directly from the waveguide, that is not over a Villary stripstanding away crosswise from the waveguide, by means of a detectorarrangement, in particular if a reflector is present at one end of thewaveguide that reflects the mechanical-elastic wave running along thewaveguide, and the detector arrangement—in particular in the proximityto this reflector—is arranged in such a position, where the amplitude ofthe wave running against the reflector as well as the amplitude of thewave reflected from there overlay amplifying themselves, whereby adoubled amplitude can be obtained in the optimal case.

Thus no Villary strip is needed, whose heat treatment and welding to thewaveguide are only with difficulty reproducible.

The position magnet should preferably possess thereby a magnetic fieldaligned parallel to the waveguide.

In this case a scanning of the useful signal is possible by a detectorarrangement, which includes in particular a detector coil, without thisdetector coil being flowed through permanently by a direct currentand/or without an additional bias magnet has to be arranged close to thedetector arrangement.

Several concrete embodiments are possible thereby:

The detector coil can be penetrated by the waveguide coaxially in itslongitudinal direction, or at least one detector coil, or twodiametrically to each other opposite detector coils, if necessary, canbe arranged on both sides of the waveguide in same position.

Preferably a flux guiding body is arranged in each case at the coil,whereby the flux guiding body should not get closer to the waveguidethan ¼ to ⅛ the wavelength of the waveguide, in order not to worsen theresult.

With a detector coil arranged coaxially to the waveguide the fluxguiding body can surround the coil outside except the passage for thewaveguide, or also can let a front face open, whereby then ashell-shaped partition wall is to be preferred around the waveguidebetween the waveguide and the interior periphery of the detector coil.

If the detector coil is not penetrated by the waveguide, but it isarranged beside the waveguide, the coil can be arranged with itslongitudinal axis parallel to the longitudinal direction of thewaveguide or crosswise to it, either with a coil only on a side of thewaveguide or with two, in particular identical coils, each otheropposite in relationship to the waveguide.

The flux guiding body can be thereby shell-shaped and surround thedetector coil in the outside with its longitudinal axis coaxial to thelongitudinal axis of the detector coil or it can be arranged in theinternal passage of the detector coil.

Particularly with the coil axis extending crosswise to the longitudinalextension of the waveguide, the flux guiding body must not completelyenclose the coil on its radial external faces, but an E-shaped fluxguiding body, whose central leg penetrates the coil, is likewise wellapplicable.

c) EMBODIMENTS

An embodiment in accordance with the invention is described in greaterby way of example detail hereinafter, with reference to the Figures. Thedrawings show:

FIG. 1: a plan view on the position sensor,

FIG. 2: a side view with partially sectioned coil in accordance withFIG. 1,

FIG. 3: a front view in accordance with FIG. 1,

FIG. 4 a, b: the detector coil in a series circuit,

FIG. 4 c: the detector coil in a measuring bridge,

FIG. 4 d: a difference amplifier for the subsequent processing of theposition signal,

FIG. 5: sectional views through various detector arrangements,

FIG. 6: sectional views through a detector arrangement on the wave body,

FIG. 7: sectional views similar to line VII-VII in accordance with FIG.3,

FIG. 8: detector arrangement with toroidal coil,

FIG. 9: further detector arrangements, and

FIG. 10 a, 10 b: additional detector arrangements.

The FIGS. 1 and 2 show a sensor element, in which the supporting body 1is a tube with a circular cross section and it is represented stronglyshortened just like the waveguide 3 running centered therein. Inpractice these two construction units are very long in the comparison tothe diameter, since they must extend over the entire measuring range inthe measuring direction 10.

Instead of a straight-lined running waveguide in the supporting body,there might be also a curved, in particular ring-shaped and circularlycurved supporting body with a waveguide 3 lying in it, whereby themeasuring direction 10 could be no more a straight, but a curved line,for example a circle or an almost complete circle.

The waveguide 3 is held central in the insignificantly larger internalcavity of the supporting body 1 by lengthwise spaced bars or by aconstantly existing support, for example by means of one or severaltubular pieces with homogeneous or cellular structure, e.g. a foam hose21, in relationship to the inside diameter of the supporting body 1. Anisolated back conductor 22 is arranged e.g. between the outercircumference of this hose 21 and the interior perimeter of the pipe,which can serve also as an electrical back conductor.

At the front end, the left one in the FIGS. 1 and 2, the supporting body1 can be closely locked by a catch 7, and the waveguide 3 can exhibit adamping element 13 at its free front end in order not to reflectmechanical oscillations arriving there in the waveguide 3, but to absorbthem as completely as possible.

However, substantial for the invention is the rear end of the tubularsupporting body 1 and of the waveguide is 3 with the connection with ahead plate 2 arranged there, without to exist in particular thenecessity to accommodate this head plate in any form of mounting plateor housing, as only this housing or the mounting plate is connectablestably with the supporting body 1.

A recess 11 is made for this purpose at the rear end of the supportingbodies 1 over a length, which corresponds maximally to the length of thehead plate 2, either—as represented in FIGS. 1, 2 and 3—a parallel islaid shifted inward to a tangent regarding to the cross section of thesupporting body 1 and the larger part of the cross section of thesupporting body 1 separated thereby is removed. The head plate 2 is forexample glued on the remaining smaller part of the cross section, whichremains existing then in form of an extension 9.

Since the head plate 2—seen in the measuring direction 10, i. e. in theproceeding direction of the supporting body 1 and the waveguide 3—issubstantially broader than the cross section of the supporting body 1,this arrangement of the head plate 2 takes place so that it isprotruding only on one side beyond the width of the cross section of thesupporting body 1, i. e. it closes in particular on the other side withthe outside edge of the supporting body, in particular with the outsideedge of the extension 9, as it is best represented in FIG. 3.

The adhesive 14 is located thereby preferably not only between thecontact surfaces of the head plate 2 with the extension 9, but alsobetween the head plate 2 and the internal perimeter segment of thisextension 9, in order to ensure a safe gluing, and it is reachingpreferably also around the edges of the extension 9, a little bit aroundon the exterior surface of the extension 9.

The FIGS. 4 ff. and 5 show detector circuits in their concrete structureand as alternate circuit diagrams, in which the detector arrangement 105(including the detector coil 5) of the Villary detector is included.

FIG. 4 a shows the basic structure of the detector circuit 50, whichshows the detector arrangement 105 including the detector coil 5connected in series with an uncoupling impedance 26, which both aresupplied together by a power source 51. Between detector coil 5 anduncoupling impedance 26 the pick-up of the useful signal 29 takes placeby a coupling impedance 25, e.g. a capacitor.

FIG. 4 b shows a similar structure, whereby the power source 51 isreplaced by a voltage supply 32 and a constant current diode 31connected in series to it in a circuit with the detector arrangement 105and the uncoupling impedance 26.

FIG. 4 c shows a circuit, in which the detector coil of the detectorarrangement is distributed on two detector coils 5″, each of themexhibiting the half of windings and being arranged opposite in twoparallel branches with the power source equipped with the voltage supply32 and the direct current diode 31. Additionally to the respective halfdetector coil 5″, an uncoupling impedance 26 in one case as well as abridge completing impedance 16 in the other case is arranged in each ofthe two parallel branches.

In any of the parallel branches, the pick-up of a signal is done in thecenter between the two elements and it is supplied over a respectivecoupling impedance 25 to an amplifier 17, which emits the useful signal29.

FIG. 4 d shows a quadrator 33, which can be inserted for theamplification of the useful signal 29 in all of the previously describedcases.

The FIGS. 5-7 show by opposition various structural execution forms inaccordance with the invention:

In FIG. 5 a the detector coil 5 surrounding the Villary strip 4 (or thewaveguide 3) is represented, from whose passage the Villary strip isprotruding on both sides. The connection of the Villary strip 4 to thewaveguide as well as the further components of the detector arrangementare not represented.

In opposition to the state of the art, in which this detector coil 5 isused for taking over a useful signal, in this case a current flow (biascurrent 60) is produced through the coil, by means of the d.c. supply51, in order to achieve the desired bias of the Villary strip 4, as itis evident on the basis of the drawn-in field lines 12.

Additionally, as a shielding against magnetic and electrostaticinfluences, this detector coil 5, preferably also the entire detectorarrangement 105, thus e.g. including the power source 51, can besurrounded as closely as possible by a shielding sleeve 61, having inthis case only the openings for the entrance of the Villary strip 4respectively the waveguide 3 on the one hand, as well as for theinserting of the power connections for the detector coil 5. Theshielding sleeve preferably consists of a high permeability material, inparticular a so-called Mu-metal with a permeability μ>1000.

FIG. 5 b show the way in which the detector coil 5 is surrounded by aflux guiding body 30, from which at the front side only the elementpenetrating the passage 5 a of the detector coil 5, either the Villarystrip 4 or the waveguide 3 stands out. Thus a foreign magnetic influenceof the detector coil 5 from the outside is reduced, but in particularthe magnetic induction inside the coil is increased, so thatsubstantially less magnetizing current is needed.

Additionally a bias of the Villary strip 4 respectively of the waveguide3 can be achieved by arranging one or more magnets 6, 6′, 6″, 6′″ insideand/or outside of the flux guiding body 30.

Thus FIG. 5 b 1 points, for example, with the polarity directionradially to the longitudinal direction of the detector coil 5 inside therod magnets 6 (or a ring magnet), arranged at the front side within theflux guiding pieces 30, whose polarity of the appropriate magnets at theopposite faces of the coil 5 is opposite to each other, in order toachieve a lateral flux (kidney-shaped field lines 12, as represented inFIG. 5 a).

The arrangement of the magnet(s) 6′- 6′″ is also possible outside, e.g.on the external front surface of the flux guiding body 30, and/or inappropriate way at the front side on the slot for the conductorconnections, as shown in FIG. 5 b 2, whereby preferably two magnets 6″,6′″ are arranged again with radial pole direction close to thelongitudinal ends outside on the lateral surface of the shielding fluxguiding pieces 30, with opposite pole direction, while a third magnet 6′is arranged at the external front side, pointing to the central openingfor entering of the waveguide 3 respectively of the Villary strip 4,likewise radially polarized. The magnets 6′ and 6″ serve primarily theamplifying of the position signal, while the magnet 6′″ serves theimprovement of the relationship between the useful signal and spurioussignals. In all three cases there are preferably permanent magnets, justlike with the magnet 6 within the flux guiding pieces 30.

In this context the detector coil 5 is used preferably only to pick upthe useful signal in form of a voltage variation, or additionally alsofor subjecting with bias current.

FIG. 5 c shows a solution, with which the detector coil 5 is surroundedalso by a flux guiding body 30, from which the Villary strip 4 is ledout only, and additionally the terminals for the detector coil 5, whichis flowed through in this case additionally by a current, in order toproduce the desired bias of the Villary strip 4.

Outside on the flux guiding body 30, which can stand over for thispurpose to some extent at the front surfaces radially outward, anadditional field coil 24 is applied. The useful signal can be picked upalternatively at the detector coil 5 or at the field coil 24respectively both signals become supplied to an evaluation circuit.

FIG. 6 shows a physical solution when applying the detector coil 5 onthe waveguide 3. Also in this case the coil 5 is as far as possibleenclosed by a flux guiding body 30, which is penetrated at the frontside in particular only by the waveguide 3, whereby an additionalsleeve-shaped bearing element 37 is arranged between the waveguide 3 andthe passage opening in the shielding 30. The bearing element 37 shouldexhibit as small a damping effect as possible in relationship to themechanical-elastic wave, which runs along the waveguide. Additionallythe tubular back conductor 22, surrounding the waveguide 3 as well asits support, e.g. the foam hose 21, is connected electricallyconductively with a front plate 39 made of electrically conductiblematerial covering the entire neighboring front surface of the fluxguiding body 30.

Further the electrical connections for the detector coil 5 are ledoutward through the flux guiding body 30.

Also here the detector arrangement 105 can be arranged additionallyoutside by an as closely as possible enclosing shielding sleeve 61,similarly to the representation and description in FIG. 5 a, with whichin this case preferably also the passage between the back conductor 22and the front plate 39 is still inside of this shielding sleeve 61.

The FIG. 7 show longitudinal sections through the detector arrangement105 surrounded by a flux guiding body 30 with the detector coil 5.

In both variants of the FIGS. 7 a, b, the detector coil 5 is penetratedin longitudinal direction by the Villary strip and stands out at bothends from the detector coil 5. In order to avoid a mechanical contactbetween both components, the Villary strip 4 can be surrounded at leastover the entire length not only of the detector coil 5 but also of theflux guiding body 30 by an e.g. hose-shaped bearing element 15 with lowmechanical damping.

Opposite to this, the flux guiding body 30 exhibits differentconfigurations in both cases:

In FIG. 7 a, the flux guiding body 30 consists of a pot-shaped base part133 in which an opening 5 a is arranged central at the front face tolead through the Villary strip 4 with surrounding hose 15. The oppositeopen front face is closed by a cover 132, which exhibits eccentrically aconductor opening 5 b′ for the two conductors to the detector coil 5,besides of a central opening 5 a′ for the stepping out of the bearingelement 15 and the Villary strip 4.

Independently from the design of the flux guiding body 30, the conductoropening 5 b can be arranged also in the lateral surface of the fluxguiding body.

This is the case with the design in accordance with FIG. 7 b, in whichthe cylindrical housing of the flux guiding body 30 consists of two halfshells, whose contact surface is the drawing surface of the FIG. 7 b,and with which all openings, thus the front side central openings 5a,a′, as well as the conductor opening 5 b,b′, are on this contact planeand are configured preferably as a half in each of the two half shells.In order to be able to use identical parts, therefore the conductoropening 5 b is present on two each other opposite positions in thelateral surface.

The FIG. 8 show a solution of the detector arrangement 105, where thedetector coil exhibits the form of a toroidal coil 205. The remainingconstruction units of the sensor are not represented in the FIG. 8,however the central passage 5 a of the detector arrangement 105 shouldbe penetrated centrally by the magnetoelastic element, thus thewaveguide itself or the Villary strip, even with these solutions of theFIG. 8.

FIG. 8 a shows the toroidal coil 205 individually, wound on atoroid-shaped coil core.

The toroidal coil 205 is surrounded in accordance with FIG. 8 c by aflux guiding body 130, which likewise exhibits a passage 5 a at itsfaces, encloses also the toroidal coil 205 and leaves only small exitopenings for the electrical connections of the coil. The flux guide 130consists of two preferably identical half shells 131, which are setopposite to each other with their open sides and accommodate inside thetoroidal coil 205, that is why the half shells 131 preferably alsopossess a round cross section, and are closed on a face except thepassage opening 105.

The FIG. 9 show detector arrangements 105, which scan the waveguidedirectly, and not a Villary strip arranged at the waveguide.

Preferably with these solutions of the FIG. 9, a direct current chargingof the detector coil 5 is abandoned, as well as to a magnet arrangedclose to the detector coil as bias magnet.

The remanence with circular polarization, remaining in the waveguide,which became excited by the original current impulse, works as biasing.

Instead of that, the detector coil 5 of the detector arrangement 105,either enclosing the waveguide 3 or arranged beside it, is arranged atsuch a position of the waveguide in which the mechanical-elastic waverunning along the waveguide overlays with a running-back wave, reflectedat a reflector 56 at the end of the waveguide, in such a way that theamplitude is amplified. A block with high specific weight, thuspreferably made of a metal, is used as reflector 56 for this purpose.

The FIGS. 9 a and 9 b show thereby a detector coil 5 penetrated by thewaveguide, whose passage opening is so large that, no contact betweendetector coil 5 and waveguide 3 is present. The detector coil 5 isencased again by a flux guiding body 30 with then approximatelycylindrical outer circumference, which at the front side likewisepossesses ingoing and outgoing openings for the waveguide 3, whichshould not contact the waveguide 3, but should keep a sufficientdistance to it.

In an opposite way, in FIG. 9 b the detector coil 5 is enclosed by apot-shaped flux guiding body 30, which accordingly does not cover thedetector coil 5 on a front face. An additional ring wall of the fluxguiding body 30 is arranged coaxially around the waveguide 3 and spacedaway from it between the detector coil 5 and the waveguide 3.

FIGS. 9 c-9 g concern one or more detector coils 5 not surrounding thewaveguide 3, but arranged beside it:

In FIG. 9 c an e. g. sleeve shaped flux guiding body 30 is arrangedcoaxially in the inside cavity of the coil 5. The same applies to FIG. 9d, however here the detector coil 5 stands with its longitudinal axisperpendicularly to the measuring direction 10, which is the extendingdirection of the waveguide 3, at a small distance from it, withoutcontacting it. The same applies to the flux guiding body 30.

FIG. 9 e shows a doubled arrangement opposite to FIG. 9 d, thus two eachother detector coils 5 diametrically opposite in relationship to thewaveguide 3 with assigned flux-guiding bodies 30.

In FIG. 9 f—on adjustment of the coil axis of the detector coil 5perpendicularly to the waveguide 3—this detector coil 5 is located on anE-shaped flux guiding body 30, i.e. on its central freely ending leg, sothat the outside freely ending legs run as close as possible along theouter circumference of the detector coil 5 and the connecting transverseleg is arranged on the side of the detector coil 5 turned away from thewaveguide 3.

FIG. 9 g shows again a doubled arrangement in contrast thereto with twosuch units made of detector coil 5 and flux guiding body 30, mirroringeach other concerning the waveguide 3, whereby additionally the gapbetween the two free ends of the each other facing legs of the two fluxguiding bodies 30 can be filled by a closing body, whereby the closingbody can be in particular likewise a flux guiding body 30 with thematerial properties defined before.

Also here again, in particular with the solutions in accordance with theFIGS. 9 b-9 g, with which no tight enclosing is given to the detectorcoil by the flux guiding pieces 30, the detector coil including the fluxguiding pieces, in particular the entire respective detector arrangement105, may be arranged by an additional shielding case 61, similarly tothe representation and description in the FIG. 5 a, for an additionalmagnetic and electrostatic shielding.

The FIGS. 10 a, 10 b show further a solution similar to FIG. 9 a,however with the difference that a distance 57 (air gap) is present inthe case of the FIG. 10 a between the detector coil 5 and thesurrounding flux guiding pieces at the front side, i. e. in axialdirection, while in the case of the FIG. 10 b a remanence body 58 ispresent between the front surfaces of the detector coil 5 and theinternal front surfaces of the flux guiding pieces 30, in particularsurrounding the waveguide 3 in a ring-shaped way.

LIST OF REFERENCES

-   1 supporting body-   2 head plate-   3 waveguide-   4 Villary strip-   4 a, b partial strip-   105 detector arrangement-   205 toroidal coil-   5 detector coil-   5′ compensation coil-   5 a opening-   6, 6′, 6″, 6′″ magnet-   7 closing flap-   9 extension-   10 measuring direction-   11 recess-   12 field lines-   13 damping element-   14 adhesive-   15 bearing element-   16 bridge completing impedance-   17 amplifier-   20 protection profile-   21 foam hose-   22 back conductor-   23 uncoupling coil-   24 field coil-   25 coupling impedance-   26 uncoupling impedance-   27 back conductor-   28 position magnet-   29 useful signal-   30, 130 flux guiding body-   131 half shell-   31 constant current diode-   32 voltage source-   132 cover-   33 quadrator-   133 base part-   37 sleeve shaped bearing element-   50 detector circuit-   51 power source-   55 compensation magnet-   56 reflector-   57 distance-   58 remanence body-   59 permanent magnet-   60 bias current-   61 shielding

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 28. (canceled) 29.(canceled)
 30. (canceled)
 31. (canceled)
 32. (canceled)
 33. (canceled)34. (canceled)
 35. (canceled)
 36. (canceled)
 37. (canceled) 38.(canceled)
 39. (canceled)
 40. (canceled)
 42. (canceled)
 43. (canceled)44. (canceled)
 45. (canceled)
 46. A position sensor according to theruntime principle of a mechanical-elastic wave, said sensor comprising:a waveguide; a position element movable along the waveguide; and adetector arrangement arranged on the waveguide including a detector coiland a power source so that a current flows through the detector coil.47. A sensor according to claim 1 wherein the power source isadjustable.
 48. A position sensor according to the runtime principle ofa mechanical-elastic wave said sensor comprising: a waveguide; aposition element movable along the waveguide; and a detector arrangementarranged on the waveguide including a detector coil and at least onecompensation magnet assigned to the waveguide in the proximity of thedetector arrangement.
 49. A position sensor according to claim 3 whereinsaid compensation magnet is positioned between the measuring range ofsaid waveguide and said detector arrangement.
 50. A position sensoraccording to claim 3 wherein said compensation magnet is arranged with aflux direction parallel to an extending direction of said waveguide. 51.A process to determine the position of a position element relative to awaveguide of a position sensor according to the runtime principle saidprocess comprising: subjecting a detector coil to a bias by directcurrent for the amplifying of a useful position signal.
 52. Processaccording to claim 6 wherein bias is controlled in such a way that theuseful position signal is optimized regarding its amplitude and/or inits relationship to a spurious position signal.